(a) A sample of a radioactive isotope contains N nuclei at time t. At time (t + At), it contains (N-AN) nuclei of the isotope. For the period At, state, in terms of N, AN and At, (i) the mean activity of the sample, activity = (ii) the probability of decay of a nucleus. probability = [1] [1] (b) A cobalt-60 source having a half-life of 5.27 years is calibrated and found to have an activity of 3.50 x 105 Bq. The uncertainty in the calibration is ±2%. Calculate the length of time, in days, after the calibration has been made, for the stated activity of 3.50 x 105 Bq to have a maximum possible error of 10%.

(a) A sample of a radioactive isotope contains N nuclei at time t. At time (t + At), it contains (N-AN) nuclei of the isotope. For the period At, state, in terms of N, AN and At, (i) the mean activity of the sample, activity = (ii) the probability of decay of a nucleus. probability = [1] [1] (b) A cobalt-60 source having a half-life of 5.27 years is calibrated and found to have an activity of 3.50 x 105 Bq. The uncertainty in the calibration is ±2%. Calculate the length of time, in days, after the calibration has been made, for the stated activity of 3.50 x 105 Bq to have a maximum possible error of 10%.